The invention is based on a hand power tool for grinding, polishing, or the like, as generically defined by the preamble to claim 1.
It is known for a hand power tool of the type defined above to be designed such that with it, both a grinding wheel motion of an oscillating grinder and a grinding wheel motion of an eccentric grinder can be achieved. The grinding wheel motion of an oscillating grinder is characterized by an orbital motion, which is also called eccentric motion, while the grinding wheel motion of an eccentric grinder is characterized by an orbital motion and a rotary motion. A hand power tool that can be used as both an oscillating grinder and an eccentric grinder is a so-called multipurpose grinder.
The choice of the particular grinding wheel type of motion in such hand power tools is made by attaching a suitably embodied grinding plate.
The invention is based on a hand power tool for grinding, polishing, or the like, having a drive motor, a gear coupled with the drive motor, and a grinding wheel operatively connected to the gear.
It is proposed that the gear has a switch device, by means of which at least two types of grinding wheel motion can be preselectable. A hand power tool embodied in this way has the advantage that the tool can be adapted, without assembly operations, to the particular type of motion of the grinding wheel required, without changing the grinding wheel. Thus the hand power tool of the invention offers great ease of use and great flexibility in terms of the conditions under which it is used.
In an advantageous embodiment of the hand power tool of the invention, in at least one selectable type of motion, an orbital motion of the grinding wheel is effected. In that case, for at least one preselectable operating mode, an oscillating grinder is available to the user.
In at least one preselectable type of motion, a self-rotation of the grinding wheel can be effected. The rotation can be tripped either by the orbital motion of the grinding wheel, or, if the grinding wheel is in a freewheeling mode with regard to a rotation, the rotation can be tripped by the operation of machining a surface. With a freewheeling mode relative to rotation, an especially high quality of the surface treated by means of the power tool can be achieved, since because the grinding wheel can optionally yield rotationally to resistance, the freewheeling mode leads to gentle surface treatment.
If an orbital motion of the grinding wheel trips a self-rotation of the grinding wheel, the grinding wheel is subjected to a so-called forced drive. As a rule, this happens in such a way that via an armature shaft of the drive motor and an eccentric sleeve connected to the drive motor, an additional self-rotation is forced on the grinding wheel.
However, it is also conceivable for a purely rotary motion or exclusively a self-rotation of the grinding wheel, for example, to be preselectable by means of the switch device.
It is also conceivable that by means of the switch device, various eccentric strokes or various rotary speeds of the grinding wheel can be preselected.
In a preferred embodiment of the hand power tool of the invention, the switch device cooperates with two gear wheels that mesh with one another, of which one is connected to the grinding wheel.
The hand power tool of the invention can be designed such that a rotation of at least one of the gear wheels can be prevented by means of the switch device. Thus the rotational behavior of the two gear wheels and the relative motion of them to one another can advantageously be varied, and the type of motion of the grinding wheel can thus be set.
A structurally particularly simple, space-saving embodiment of the hand power tool of the invention is obtained if the first gear wheel connected to the grinding wheel has a set of external teeth, which meshes with a set of internal teeth of the other gear wheel. In that case, the first gear wheel is embodied as a so-called planet wheel, and the second gear wheel is embodied as a so-called ring gear. By a suitable selection of gear wheels, a gear ratio can be set that advantageously allows a high oscillating frequency of the grinding wheel, at a simultaneously low rotary speed of the grinding wheel.
Expediently, the gear wheel having the internal teeth is disposed in a slide bearing ring. On the one hand, this gear wheel is thus supported in a space-saving way, and on the other, there is the advantage that upon rotation of this gear wheel, only slight frictional forces have to be overcome. However, it is also conceivable for instance for the gear wheel with the inner teeth to be disposed in a roller bearing.
A structurally especially simple embodiment of the hand power tool of the invention is obtained if the switch device includes at least one locking bolt, which cooperates with at least one recess in the first gear wheel or in the second gear wheel. By means of such a locking bolt, it is simple to prevent a self-rotation of the respective gear wheel. In the case of a gear wheel with external teeth, embodied as a planet wheel, which is in contact on the one hand with the drive shaft of the drive motor and on the other with the grinding wheel, is eccentrically supported, and meshes with the inner teeth of a ring gear, the engagement of the locking bolt with the recess of the planet wheel, which recess, to compensate for the eccentric driving motion expediently has a larger diameter than the locking bolt, causes an oscillating grinding motion, or a purely orbital motion of the grinding wheel, with the ring gear in the slide bearing ring being carried along in sliding fashion.
However, if the locking bolt engages a recess of the ring gear, thus preventing the rotation of the ring gear in the slide bearing ring, then a self-rotation is imposed on the planet wheel upon its eccentric motion. Hence a self-rotation of the planet wheel is superimposed on the eccentric motion of the same planet wheel.
If the locking bolt engages neither a recess of the planet wheel nor a recess of the ring gear, then the planet wheel is in the freewheeling mode. The grinding wheel connected to the planet wheel can thus also rotate freely.
Preferably, the switch device includes two locking bolts, namely a first locking bolt for engaging a recess of the first gear wheel and a second locking bolt for engaging a recess of the second gear wheel.
Advantageously, for shifting the at least one locking bolt, the switch device has a switching ring. The switching ring acts as the actuating device for the at least one locking bolt. The switching ring is supported for instance in a preferably two-part housing of the gear and is actuatable in the circumferential direction.
Preferably, the switching ring has at least one axial, circular-arclike recess, in which a locking bolt is guided. If the switch device has two locking bolts, then the switching ring preferably has two recesses, with one locking bolt guided in each recess.
Advantageously, the switching ring, in the region of the axial, circular-arclike recess, has a ramplike chamfer, by means of which the at least one locking bolt is axially shiftable by rotation of the switching ring. By suitable disposition of the chamfers, it is possible for one locking bolt, resting with a region of increased diameter on the top side of the switching ring, to engage a recess of the first gear wheel in one position of the switching ring, and for the other locking bolt, in a different position of the switching ring, to engage a recess of the second gear wheel.
In order to keep the at least one locking bolt in position, the locking bolt is urged in the axial direction by means of a spring.
An especially simple embodiment of such a spring pertains in the case of a sheet-metal spring, which engages a recess or slot in the locking bolt and axially loads the locking bolt.
The switching ring can be manually actuated, so that it can be put into whichever switching position is desired by simple manual shifting, or it can be actuated by a control and/or regulating unit via an actuator.
To allow convenient use of the hand power tool of the invention on many surfaces of different outlines without changing the grinding wheel, the grinding wheel preferably has an outline which has at least one straight boundary edge and at least one curved boundary edge.